The present invention relates to a disc brake for use on a motor vehicle.
More particularly, the present invention relates to a disc brake which comprises a fixed torque taking or carrier member which straddles a rotatable disc and carries both a directly and an indirectly actuated friction pad assembly. A brake housing overlies the torque taking member and is guided for sliding movement towards and away from the disc by guide pins which are fixed to the torque taking member and which are slidable in openings arranged in the brake housing in a conventional manner. The brake housing comprises a main body portion which contains an actuator mechanism, and a bridge section integral therewith ie. the bridge section is bolted to the main body portion or integrally cast therewith so as to be of unitary construction. The bridge section has an opening arranged radially of the disc, through which the friction pad assemblies can be inserted and removed from the torque taking member.
The present invention relates more specifically to a disc brake wherein the actuator mechanism comprises at least one, but preferably two tappets which are axially movable towards the brake disc to engage and press the directly actuated friction pad assembly against one side of the braking disc, the brake housing reacting and sliding on the said guide pins to apply the indirectly actuated friction pad assembly to the other side of the braking disc. Actuation of the brake is by way of a lever and eccentric arrangement wherein the eccentric arrangement engages the said tappets, pivotal movement of the lever causing the eccentric arrangement to move the tappets towards the braking disc.
In the above described type of disc brake certain problems occur in known constructions and it is the aim of the present invention to seek to overcome these problems to improve performance, life and ease of manufacture.
One such problem relates to the support of the adjustable tappets. In known constructions the adjustable tappets are supported in bearings in the brake housing. However, appreciating that each such tappet is an elongate assembly, it is usual for the bearing length to be less than optimum. As a result and noting the fact that the geometry of the brake actuator is such that the eccentric arrangement which engages the tappets exerts a side load on each of the tappets when the brake is actuated, the tappets will, in certain circumstances, experience side forces such as to cause them to tilt. This tilting may be accentuated by a combination of the tappets extending as a result of lining wear and also as a result of the clearances which exist between the outer wall of the tappet and its respective bearings. Tilting of the tappets may result in unwanted taper wear of the friction pads, and in addition, undesirable wear on the related components of the tappets, supporting bearings and adjacent mechanisms.
The aim of this aspect of the present invention it to produce a new brake design which minimises if not overcomes, the above problem.
According to a first aspect of the present invention there is provided a disc brake comprising a brake housing which, in use, straddles a braking disc and is slidably mounted on a torque taking member, so as to be movable towards and away from the braking disc, the brake housing incorporating a brake actuator mechanism located on one side of the braking disc and arranged to directly engage a friction pad assembly carried by the torque taking member on one side of the braking disc, another friction pad assembly being likewise carried by the torque taking member on the other side of the braking disc, the brake actuator mechanism comprising at least one adjustable tappet assembly which can be engaged with the directly actuated friction pad assembly under the action of a lever and eccentric arrangement, the actuator assembly being located within a recess in the brake housing, which recess is open towards the braking disc, and closed by a cover plate secured to the brake housing, the tappet extending through a bearing aperture in the cover plate, which bearing aperture extends as the inside wall of a cylindrical projection integrally formed with the cover plate, the cylindrical projection extending into the said recess of the brake housing for the major portion of the length of said tappet.
Thus, by virtue of this axially extended bearing the or each tappet is better supported along its length, this improved support resisting tilting of the tappet, and improving actuation efficiency and adjuster control.
In a preferred embodiment the brake comprises two adjustable tappet assemblies, each tappet being basically a two part assembly, one part being a female part which is generally cylindrical with an enlarged diameter head at one end region thereof, this enlarged diameter head engaging, in use, the directly actuated friction pad assembly. Extending from the other end of the said female part, through said female part, is an axially extending blind bore within which one end region of the other part of the tappet assembly ie. the male part, is threadedly engaged, the male part likewise having an enlarged head region which is, in use, engaged and acted upon by the said eccentric arrangement. This enlarged head forms a bearing surface which engages a wall of the axially extending cylindrical projection integrally formed with the cover plate.
Thus, appreciating that the major portion of the outer surface of the female part of each tappet assembly is supported along its length by the inner wall of a said cylindrical projections, thus resisting tilting of the tappet assembly, the engagement of the said bearing surface of the enlarged head of the said male part, with said cylindrical projection further improves tappet support and resists any possibility of tilting under the action of the eccentric arrangement.
Preferably this enlarged head has at its radially outer edge region, an axially extending lip which extends towards the threaded end region of the said male part and forms a cylindrical inner bearing surface which engages around the outer wall formed by the said axially extending cylindrical projection which is integrally formed with the cover plate. Alternatively the free end region of the said cylindrical projection has an enlarged internal diameter section which engages around the outer peripheral bearing surface of the said enlarged head of the said male part.
Whilst the cylindrical projections or extensions of the cover plate may be cast with the cover plate to thus form a unitary construction, the cylindrical extensions may alternatively be at least partially formed by cylindrical bearing sleeves which are secured to the cover plate. Thus the cylindrical bearing sleeves and cover plate may be made from different materials ie. the bearing sleeves may be made of a more suitable and probably more expensive bearing material such as a sintered bearing material and may be cast into the cover plate which can itself be formed as a die casting, thus optimising the construction.
Further, whilst the axially extending lip of the head reigon of the preferred form of said male part of each tappet assembly may be integrally formed with the said male part to thus form a unitary construction, the axially extending lip may alternatively be formed by an appropriately dimensioned hollow cylindrical member in the form of an annulus, which can be secured to the outer surface of the head region of the said male part.
Located between the two tappets is preferably an adjuster mechanism which is preferably secured in position in a further cylindrical projection of the cover plate, which further cylindrical projection is preferably cast with the cover plate to form a unitary construction. This adjuster mechanism incorporates a gear wheel which meshes with teeth provided on the respective heads of the respective male parts of said tappets so that rotation of the gear wheel adjusts both tappetsxe2x80x94rotation of the male parts causing the said female parts which are keyed in the cylindrical bearing projections, to move axially through the bearing apertures towards the directly actuated friction pad assembly.
The adjuster mechanism is preferably actuated via gear teeth provided on the lever and eccentric arrangement, a lost motion mechanism being incorporated so that only after sufficient movement of the lever does a further gear wheel with which the gear teeth mesh, cause the first mentioned gear wheel to rotate and the tappets to be adjusted.
The or each said female part may be keyed in a respective cylindrical bearing projection by one or more splines extending axially of the or each said female part and cylindrical bearing projection. The splines may be provided on said female part with complementary grooves being provided in the inner wall of said cylindrical bearing projection. Alternatively the splines could be located in the inner wall of the said cylindrical projection, with the complimentary grooves in the outer wall of said female part.
In an alternative construction, the or each said female part may be keyed in a respective cylindrical bearing projection by the bearing aperture on the or each cylindrical bearing projection having a non-circular/cylindrical transverse cross section and the or each female part having a complimentary transverse cross section outer profile. Preferably the bearing apertures and outer profile of the female parts are trilobal to prevent the female parts from rotating in the respective said bearing apertures.
This trilobal construction is considered to be easier to manufacture than a splined arrangement as it can be formed by a simple forging process on the said female part. Also if the bearing projection is formed by a cylindrical bearing sleeve secured to the cover plate, the trilobal internal configuration is easily formed with the sleeve being manufactured by way of sintering and therefore requiring a minimum amount of finishing.
Further, in a two tappet construction the tendency for the tappets to bind and/or tilt in the bearing apertures as formed by the bearing projections, as the brake experiences torque during brake applications, is minimised if the trilobal cross sections are arranged in the same orientation with the apex of one lobe of each trilobal cross section being directed towards the centre of rotation of the brake disc.
If desired, the cover plate can incorporate other cylindrical, or other configuration, projections incorporating appropriately dimensioned spigots or recesses within which various ancillary brake mechanisms eg. a pad wear sensor and/or manual retraction mechanism, can be located, and for ease of manufacture and assembly of the brake such cover plate spigots and recesses can be produced in mirror image duplication so that irrespective of the way the cover plate is initially installed, appropriate locating spigots and/or recesses will always be provided.
A further problem arises with the basic construction of the present invention with regard to the provision of appropriate bearings within the brake housing to support part cylindrical regions of the lever and eccentric arrangement.
To explain, current brake designs which use a lever and eccentric as a method of applying the brake require the cylindrical surfaces of the eccentric to be rotatably arranged in a semi-cylindrical roller bearing. A bearing cage is in these prior constructions, seated in a complimentary profiled form machined in the cover plate. However, in these brakes the cover plate is mounted on the rear of the brake housing ie. away from the braking disc, and as the cover plate is a separate component this presents easy access for tooling for forming the relevant machined surfaces to seat the semi-cylindrical bearings, though it is an expensive and slow operation.
With the brake design of the present invention wherein the recess in the brake housing, which houses the actuator mechanism, opens towards the brake disc, problems occur with regard to machining of the required bearing seats. To overcome this problem it is of course always possible to provide a further outer cover plate which can be machined as per prior art constructions. However this adds to the cost of the construction. Further, a lateral opening could be provided in the brake housing wall to permit access of a suitable machining tool. However, whilst it still may be practical to produce the required surfaces in this way, we are then faced with the problem of suitably sealing the opening once the brake is assembled. Again this adds to the cost of the construction.
The aim of this further aspect of the present invention is therefore to provide a disc brake construction of the type which the present invention relates, with appropriate bearing surfaces for the eccentric arrangement.
According to a further aspect of the present invention there is provided a disc brake comprising a torque taking member which, in use, straddles a braking disc, a brake housing being slidably mounted on the torque taking member so as to be movable towards and away from the braking disc, the brake housing having a main body portion with a recess in which an actuator mechanism operable by a lever and eccentric arrangement, is mounted, the recess opening towards the braking disc and being provided with bearing seat members which are located in further respective recesses provided in a wall of the said recess of the brake housing, each bearing seat member incorporating a part cylindrical bearing surface on which a bearing forming part of the lever and eccentric arrangement can engage.
Preferably each bearing seat member is provided with a retaining projection at one end of the part cylindrical bearing surface, this retaining projection, in use, extending over an end of a groove provided in the lever and eccentric arrangement to axially retain a cylindrical force transmitting member which is arranged in said groove.
Further, the two bearing seat members are each preferably located in said further recesses so as to be freely rotatable therein about an axis perpendicular to the base of each recess. Thus, on assembly the bearing seat members can be loosely located in said further recesses with the bearing seat members being automatically correctly aligned with each other as and when the lever and eccentric arrangement is located thereon. Alternatively, the bearing seat members may be of suitable design eg. tapered base regions, to locate in suitably designed further recesses in the brake housing recess, with initial operation of the brake applying pressure to each bearing seat member via the lever and eccentric arrangement, and causing deformation of the base regions and/or further recesses, to thus provide for a secure positive location of the bearing seat members in the brake housing, correctly aligned with each other.
Further, by manufacturing the bearing seat members as separate components from the brake housing, a more suitable material for the bearing seat members can be selected without the need to make the whole brake housing of the same material. Thus the cost of construction can be minimized without any reduction in performance characteristics.
According to a further aspect of the present invention there is provided a disc brake comprising a brake housing, which straddles a braking disc and is slidably mounted on a torque taking member which carries a directly actuated and an indirectly actuated friction pad assembly located on opposite side faces of the braking disc, the brake housing being slidable towards and away from the braking disc under the action of an actuator mechanism which is housed in part of the brake housing on one side of the braking disc, the actuator mechanism comprising a pair of tappets which can engage against the directly actuatable friction pad assembly, said tappets being axially slidable towards the braking disc by a lever and eccentric arrangement, one end region of the lever having two lateral extensions, each extension forming a part cylindrical bearing surface which is supported on a bearing seat within the brake housing, a groove extending transversely of the lever between the said lateral projections, said groove being eccentric relative to said part cylindrical bearing surfaces and housing a force transmitting member towards each end region thereof, each force transmitting member engaging a respective tappet, an intermediate member located in the groove between said two force transmitting members serving to correctly position said force transmitting members with respect to the tappets and carrying a gear drive which engages with an adjuster mechanism which can operate to adjust the length of the tappets as necessary.
Preferably the groove is of part cylindrical configuration with the force transmission members being cylindrical members, the intermediate member being likewise cylindrical with the gear drive projecting laterally from the outer surface thereof. The groove may be semi-circular in transverse cross section or less than a semi-circle in transverse cross section, in which case the force transmitting members and the intermediate member can merely be located laterally within the groove during installation. Alternatively, if the groove is larger than a semi-circle, the various members have to be axially slid into the groove.
Whilst the force transmitting members are rotatable within the groove and are axially retained in position preferably by the intermediate member and the retaining projection of each bearing seat member as described hereabove, the intermediate member is preferably fixed in the groove against rotation and/or axial movement by the surface of the lever adjacent the groove being staked ie. deformed, at spaced locations along the axial length of the groove. Alternatively, the intermediate member may be axially retained in the groove, eg. by the force transmitting members, though rotatable therein to a limited extent, the rotational limit being defined by the gear drive engaging the sides of the groove, this limited rotation possibly providing for the required lost motion in the adjuster mechanism.
The lever and lateral extensions are preferably cast with the groove required to locate the force transmitting members and intermediate member, being machined in one operation. Whilst the lever and lateral extensions are preferably manufactured from cast steel, the intermediate member could, if desired, be manufactured from any other suitable metal, eg. even a plastics type of material.
The above construction provides an improved weight reduced lever and eccentric arrangement which is easy to manufacture and arranged to advantageously provide a drive mechanism to the adjuster mechanism.
According to a still further aspect of the present invention there is provided a disc brake comprising a torque taking member which straddles a braking, disc, with a brake housing being slidably mounted on the torque taking member for movement parallel to the axis of the rotatable braking disc, the brake housing, incorporating a brake actuator mechanism located on one side of the braking disc, the disc brake actuator mechanism incorporating at least one tappet assembly which is axially slidable within a bearing, aperture, the tappet assembly having an enlarged head region which can engage on brake actuation, a directly actuated friction pad assembly carried by the torque taking member on one side of the braking disc, an indirectly actuatable friction pad assembly being likewise carried by the torque taking member on the opposite side of the braking disc, a seal assembly in the form of an annular construction being secured between the brake housing, the head of the tappet and a shaft of the tappet, the annular seal assembly comprising a flexible annular boot member, one end region of which is secured in a groove in the head region of the tappet, the other end region being located between a surface of the brake housing adjacent to the bearing aperture and part of a general cylindrical retaining section which is engaged securely within an enlarged diameter end region of the bearing aperture, an annular lip seal secured to the retaining member, projecting inwardly of the bearing aperture and engaging against the said shaft of the tappet.
The above still further aspect of the present invention provides a double tappet seal which is positively secured to the brake housing and which is relatively easy to instal. In a preferred construction of the seal assembly the annular lip seal is secured eg bonded, coaxially with the annular retaining member which is preferably made of metal. The combined lip seal and retaining member are, during construction of the brake, fitted into an enlarged end region of the bearing aperture, prior to the tappet being inserted in the bearing aperture. The retaining member being an interference fit in the enlarged end region of the bearing aperture. Then the tappet with the flexible boot member secured to the head region of the tappet, is inserted through the lip seal and thus the bearing aperture, the flexible boot member then being secured between the retaining member and an adjacent surface of the brake housing.
In an alternative embodiment wherein the flexible boot member is also secured to the retaining member so that the boot member, lip seal and retaining member form a unitary construction, the flexible boot member is secured to the head region of the tappet with the lip seal located on the tappet shaft, prior to installation of the tappet in the bearing aperture. On insertion of the tappet into the bearing aperture the retaining member can be pressed into the enlarged end region of the bearing aperture as an interference fit, securing the lip seal in the desired position relative to the tappet shaft wall as well as retaining the flexible boot in the desired position.
The above individual aspects of the construction of the present invention improve the performance characteristics and ease of manufacture and can be adopted in combination with each other or individually as desired.